* Negative values of rotation period indicate that the
planet rotates in the direction opposite to that in which it orbits
the Sun. This is called retrograde rotation.

The semimajor axis (the average distance to the Sun) is given in units
of the Earth's average distance to the Sun, which is called an AU.
For example, Neptune is 30 times more distant from the Sun than the
Earth, on average. Orbital periods are also given in units of the
Earth's orbital period, which is a year.

The eccentricity (e) is a number which
measures how elliptical orbits are. If e = 0, the orbit is a circle.
Most of the planets have eccentricities close to 0, so they must have
orbits which are nearly circular.

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